1. Field of the Invention
The present invention generally relates to a viscous fluid type heat generator in which heat is generated by forcibly shearing a fluid having high viscosity (hereinafter referred to as a viscous fluid) confined in a chamber and the heat is transmitted to a heat exchanging liquid circulating through a heating system. More particularly, the present invention relates to a viscous fluid type heat generator provided with an ability to quickly change a heat-generation performance in response to a change in a requirement for either increasing or reducing heating to be applied to an objective heated area.
2. Description of the Related Art
Japanese Unexamined Utility Model Publication (Kokai) No.3-98107 (JU-A-3-98107) discloses a viscous fluid type heat generator adapted for being incorporated into an automobile heating system as a supplemental heat source. The viscous fluid type heat generator of JU-A-3-98107 is formed as a heat generator provided with a unit for changing a heat-generation performance. The heat generator of JU-A-3-98107 includes front and rear housings connected together to form a housing assembly in which a heat generating chamber for permitting a viscous fluid to generate heat, and a heat receiving chamber arranged adjacent to the heat generating chamber for permitting a heat exchanging liquid to receive the heat from the heat generating chamber, are formed. The heat receiving chamber in the housing assembly permits the heat exchanging liquid to flow therethrough from a liquid inlet port to a liquid outlet port formed in a portion of the housing assembly. Namely, the heat exchanging liquid is circulated through the heat receiving chamber and a separate heating circuit of the automobile heating system so as to supply the heat to the objective area, e.g., a passenger compartment of the automobile during the operation of the heating system. The heat exchanging liquid flows into and out of the heat receiving chamber through the liquid inlet port and the liquid outlet port. The heat generator of JU-A-3-98107 further includes a drive shaft rotatably supported by bearings which are seated in the front and rear housings of the housing assembly. A rotor element is mounted on the drive shaft so as to be rotated together with the drive shaft within the heat generating chamber. The inner wall surface of the heat generating chamber and the outer surfaces of the rotor element define labyrinth grooves in which the viscous fluid such as silicone oil having a chain-molecular structure is held to generate heat, in response to the rotation of the rotor element.
The heat generator of JU-A-3-98107 has such a characteristic arrangement that upper and lower housings are attached to a bottom portion of the housing assembly to form a heat generation control chamber therein. The heat generation control chamber is formed as a volume-variable chamber having a wall consisting of a membrane such as a diaphragm.
The heat generating chamber communicates with the atmosphere via a through-hole bored in an upper portion of the front and rear housings of the housing assembly, and with the heat generation control chamber via a communicating channel arranged between the heat generation control chamber and the heat generating chamber. The volume of the heat generation control chamber is adjustably changed by the movement of the diaphragm which is caused by a spring element having a predetermined spring factor or an externally supplied signal such as a pressure signal supplied from an engine manifold of an automobile.
When the drive shaft of the heat generator of JU-A-3-98107 incorporated in an automobile heating system is driven by an automobile engine, the rotor element is rotated within the heat generating chamber, so that heat is generated by the viscous fluid to which a shearing force is applied between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. The heat generated by the viscous fluid is transmitted from the heat generating chamber to the heat exchanging liquid, i.e., engine-cooling water circulating through the heating system and carried by the water to a heating circuit of the heating system to warm an objective heated area such as a passenger compartment.
When it is detected that the objective area is excessively heated with respect to a reference temperature value predetermined for that area, through the detection of the temperature of the viscous fluid, the diaphragm of the heat generation control chamber is moved in response to a vacuum pressure signal supplied from the engine manifold to increase the volume of the heat generation control chamber. Accordingly, the viscous fluid is withdrawn from the heat generating chamber into the heat generation control chamber to reduce generation of heat by the viscous fluid between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. Therefore, the heat generation performance can be reduced, i.e., the provision of heat to the objective heated area is reduced.
When it is detected that heating of the objective heated area is excessively weak with respect to the predetermined reference temperature value, through the detection of the temperature of the viscous fluid, the diaphragm of the heat generation control chamber is moved by the pressure signal and by the spring force of the spring element to reduce the volume of the heat generation control chamber. Therefore, the viscous fluid contained in the heat generation control chamber is supplied into the heat generating chamber so as to increase heat generation by the viscous fluid between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. As a result, the heat generation performance can be increased, i.e., the provision of heat to the objective heated area is increased.
Nevertheless, in the viscous fluid type heat generator having variable heat generation performance, disclosed in the JU-A-3-98107, when the viscous fluid is withdrawn from the heat generating chamber into the heat generation control chamber, atmospheric air is introduced from the through-hole of the housing assembly into the heat generating chamber so as to remove a vacuum occurring in the heat generating chamber due to the withdrawal of the viscous fluid therefrom. Thus, the viscous fluid must come into contact with the atmospheric air many times when the change of the heat generation performance occurs, and is oxidized. Therefore, a gradual degradation of the heat generating characteristics of the viscous fluid occurs. Further, the above-mentioned through-hole formed in the housing assembly permits a certain amount of moisture to enter from the atmosphere into the heat generating chamber of the heat generator, and accordingly, the viscous fluid is adversely affected by the moisture within the heat generating chamber after a long operation time of the heat generator, so that the heat generating characteristics of the viscous fluid must be again degraded.
Further, the viscous fluid type heat generator of JU-A-3-98107 is provided with internally neither a mechanism nor a means for conducting an appropriate replacement of the viscous fluid between the heat generating chamber and the heat generation control chamber. Thus, when the drive shaft is continuously rotated at a high speed without withdrawing the viscous fluid from the heat generating chamber into the heat generating control chamber, the viscous fluid confined in the heat generating chamber is continuously subjected to a shearing action by the rotor element and heated to an extremely high temperature at which the physical properties of the viscous fluid are degraded, reducing the heat generation performance.
U.S. Pat. No. 4,974,778, and the corresponding German laid-open publication DE-3832966 disclose a different type of heating system for a vehicle with a liquid-cooled internal combustion engine, which includes a viscous fluid type heating unit. The viscous fluid type heating unit of U.S. Pat. No. '778 includes a housing defining a heat generating chamber or a working chamber having a through-opening, and a heat generation control chamber or a viscous fluid supply chamber communicating with the heat generating chamber via the through-opening. The through-opening between the heat generating chamber and the heat generation control chamber is closed and opened by a spring-operated closing means, and accordingly, the degradation of the viscous fluid can be avoided even after either the extended use of the heating unit or a high speed continuous operation of the heating unit. The spring-operated closing means of the heating unit of U.S. Pat. No. '778 is provided with a lever member having one pivotally supported end and the other free end to which a closing member is attached to be able to close the through-opening, a resilient member for constantly urging the closing member toward the through-opening via the lever member, and a leaf spring made of a bimetallic material deformable in response to a change in the temperature of the viscous fluid and attached to the lever member so as to be deformed against the spring force of the resilient member. Thus, a thermal deformation of the bimetallic leaf spring causes the lever member to pivotally move to cause the closing member held by the lever member to be moved toward and away from the through-opening between the heat generating chamber and the heat generation control chamber against the spring force of the resilient member. However, the employment of a plurality of the operating members for constituting the closing means to close the through-opening between the heat generating chamber and the heat generation control chamber causes the unfavorable operating condition that a deformation of the bimetallic leaf spring due to a change in the temperature of the viscous fluid within the heat generation control chamber does not cause an immediate movement of the closing member toward and away from the through-opening. Further, a controlling operating of the closing means might become inaccurate due to total manufacturing tolerances of all of the plurality of operating members of the closing means. Namely, the performance of the closing means of the through-opening of the viscous fluid type heating unit of U.S. Pat. No. '778 is insufficient for controlling the heat generation performance of the viscous fluid type heating unit quickly and accurately. Further, the use of the plurality of operating members to constitute the closing means of the through-opening between the heat generating chamber and the heat generation control chamber causes an increase in not only the manufacturing cost of the closing means but also a difficulty in assembling the closing means in the heating unit of the heating system. Moreover, the closing means of the viscous fluid type heating unit of U.S. Pat. No. '778 has a relatively large size requiring a large volume of the heat generation control chamber to receive therein the closing means. As a result, the mounting of the viscous fluid type heating unit in a vehicle at a position suitable for receiving drive power from the vehicle internal combustion engine must be difficult.
By taking into consideration the above-mentioned various defects of the viscous fluid type heating units according to the prior art, the present inventors have sought measures for solving the defects of the viscous fluid type heating unit according to the prior art, and have considered to employ a flap valve capable of deforming itself in order to open and close a through-opening arranged between a heat generating chamber and a heat generation control chamber of a viscous fluid type heat generator having a variable heat generation performance. Nevertheless, it was confirmed that an arrangement of the flap valve in the heat generation control chamber to control the opening and closing of the through-opening between the heat generating chamber and the heat generation control chamber is still insufficient for obtaining accurate and rapid response performance in controlling the heat generation performance of the viscous fluid type heat generator. Namely, when a flap valve was disposed so as to openably close an end opening of a fluid withdrawing passage, a large contact area appeared between the flap valve and a contacting area surrounding the end opening of the fluid withdrawing passage. This is because the flap valve is an element usually having a flat contacting face, and the end opening of the fluid withdrawing passage is usually formed to have a flat peripheral region surrounding thereof. Thus, the flap valve cannot easily move from its closing position to its opening position due to a large surface tension of the viscous fluid acting between the large contacting face of the flap valve and the large contacting area surrounding the end opening of the fluid withdrawing passage. This unfavorable condition of the flap valve occurs irrespective of a difference in the type of the flap valve between a reed type flap valve which is deformable in response to a change in a pressure prevailing in the heat generating chamber and a thermally operative bimetallic flap valve.
Further, it was also confirmed that when a flap valve is arranged to openably close an end opening of a fluid supply passage, an identical unfavorable operating condition appears in the case where the flap valve is a thermo-sensitive bimetallic flap valve. Thus, the employment of the flap valves for controlling the opening and closing the end openings of the fluid supply and withdrawing passages of the viscous fluid type heat generator was insufficient for obtaining an accurate and quick controlling of the heat generation performance of the heat generator.